Hello ,
Form what you mentioned , you might be having teeth grinding habit (obviously unconsciously) that is the reason why your teeth are sensitive when you touch them by nail as their might be a small layer of Denton covering the nerve .
Another possibility which is rare is the tooth might have got fractured (horizontally )
Next Steps
Go to the dentist
Health Tips
Take some desensitising tooth paste apply on the teeth which feel cut down n keep for 2mins and then rinse it off , this might help in reducing the sensitivity .